As a background art of this technology field, there is LTE (Long Term Evolution) which is a cellular system to which OFDMA (Orthogonal Frequency Division Multiple Access)-MIMO (Multiple Input Multiple Output) technology is applied. For example, 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures,” TS36.213, v9.0.1, 2009/12 discloses a communication procedure in a radio physical layer between a base station apparatus and user equipment; 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification,” TS36.331, v9.1.0, 2009/12 discloses a signaling method between a base station apparatus and user equipment. By performing MIMO transmission between the base station apparatus and the user equipment and allocating respective resource blocks each of which bundles subcarriers of the OFDM to separate user equipment, it is possible for LTE to attain a high throughput by a synergistic effect of space division multiplexing and wide-band OFDMA. However, since the so-called cell-edge terminal which is located at a position away from the base station apparatus uses the same frequency with multiple base station apparatuses, its throughput lowers because the cells formed by the respective base station apparatuses interfere mutually and because the radio transmission attenuation due to an increased distance from the base station apparatus becomes large.
There is macro diversity as one of methods of improving the communication quality of the cell-edge terminal. This aims at communication quality improvement at the cell edge by transmitting data between multiple base station apparatuses and a single piece of the user equipment and is disclosed, for example, by Japanese Unexamined Patent Application Publication No. H8 (1996)-186857. This patent document discloses a method where, by the user equipment receiving predetermined signals transmitted with predetermined powers from multiple base station apparatuses, respectively, and synthesizing these signals, the communication quality after the synthesis in a radio circuit between the respective base station apparatuses which are connected simultaneously is estimated, and a connection control with the base station apparatuses is performed based on the estimated result. That is, it is a technology whereby the communication quality is compared between a case where signals from multiple base station apparatuses are synthesized and a case where it is not synthesized, and if the communication quality improvement by synthesizing is expected to a certain amount or more, a connection control to the base stations is performed.
There is a distributed antenna system as one of other methods of improving the communication quality of the cell-edge terminal. For example, as is disclosed by Japanese Unexamined Patent Application Publication No. H11 (1999)-261474, a system configuration method where the antennas are arranged in a distribution manner and a centralized control apparatus performs a signal processing is known. In this patent application, there is disclosed a distributed antenna system characterized by having selection means for selecting at least one of multiple antenna parts, and beam formation means for forming a transmitted beam or a received beam by setting an arbitrary excitation condition to the antenna part selected by this selection means. That is, this is a technology of preventing interfering radiation to a third party resulting from the use of an unnecessary antenna and increase in interference signal which should be eliminated at the reception side when forming a beam to the user equipment.
In order to improve the communication quality, it is necessary to improve at least SINR (Signal to Interference plus Noise Ratio). However, if multiple signal supply sources are allocated to a single terminal like macro diversity, it will lose other communication opportunities by that amount, and, as a result, the throughput will fall. Therefore, it is possible to improve the throughput of the terminal by allocating separate signal supply sources to the terminals and making the plurality terminals simultaneously communicate as a system, even if suppressing the degree of improvement of SINR. As a technology which pays attention to a fact that the terminal throughput is in a trade-off relationship between the number of terminals and SINR, Japanese Unexamined Patent Application Publication No. 2010-010968 is known, for example. The present application discloses a radio communication method which is an antenna group switching method whereby a current antenna group used for radio communication among multiple antenna groups including a part of or all of multiple antennas provided in the base station is dynamically switched, characterized in that the number of accommodated users which is the number of the communication terminals currently under communication is monitored, the number of accommodated users is compared with the number of accommodatable users which is the largest number of communication terminals such that a value representing the communication quality of the antenna within the current antenna group can be maintained to have a predetermined threshold, and the antenna group having the smallest number of accommodatable users which exceeds the number of accommodated users is decided to be a current antenna group. That is, it is a terminal count adaptive control technology which provides a radio communication service to the terminals with a fewer number of antennas as the number of accommodated terminals becomes larger, and which provides the radio communication service with a higher SINR using a large number of antennas as the number of accommodated terminals becomes smaller.